The present invention relates to functional polyamic acid microfine particles, functional polyimide microfine particles, and processes for their production. The invention further relates to a method for qualitative analysis of the surface of polyimide microfine particles.
Polyimides are not only favorable in mechanical properties but also satisfactory in other properties such as heat resistance, resistance to chemicals, and electric insulating properties and have, therefore, been used broadly as electrical/electronic materials, car component materials, and substitutes for metals and ceramics, among other applications.
The conventional process for synthesizing a polyimide comprises reacting a tetracarboxylic dianhydride with a diamine in a solvent such as N,N-dimethylformamide (DMF) to give a polyamic acid which is a precursor of the objective polyimide in the form of a varnish, and subjecting this varnish to precipitation to provide the objective polyimide as fine powders.
However, this technology has the drawback that the polyimide particles separating out with the progress of polymerization reaction undergo coalescence/coagulation, thus failing to give a monodispersed polyimide system.
An alternative technology comprises polymerizing a tetracarboxylic dianhydride with an organic diamine in an organic solvent to give a polyamic acid solution, pouring this solution in a poor solvent for the polymer, recovering the resulting precipitate, and subjecting it to thermal cyclization reaction to provide the objective polyimide.
However, when a microfine polyimide powder is to be produced by this technology, the polymer block must be recovered after the imidation reaction and mechanically pulverized, thus introducing a complicating factor into the production process. Moreover, mechanical pulverization yields only more or less coarse particles and can hardly provide a monodispersed system of discrete particles. In addition, the above technology does not lend itself well to the control of particle morphology and size distribution. Therefore, there has been a standing demand for development of a technology for producing a microfine polyimide powder capable of providing a monodispersed system.
Furthermore, such polyimide microfine particles with controlled shape and size distribution can be expected to find application in a variety of new uses should they be provided with various characteristics.
A primary object of the present invention, therefore, is to provide processes for producing functional polyamic acid microfine particles and functional polyimide microfine particles by which such particles can be controlled critically in particle shape and in particle size distribution. A further object of the present invention is to provide polyamic acid microfine particles and polyimide microfine particles both having good monodispersibility and carrying functional groups at least on the particle surface.
With a view to overcoming the above drawbacks of the prior art, the inventors of this invention explored in earnest for a way to accomplish the above object and discovered that the above object can be accomplished by using a process including a certain procedure herein defined. This invention has been developed on the basis of the above finding.
The present invention, therefore, is directed to the following functional polyamic acid microfine particles, functional polyimide microfine particles and processes for producing said particles.
1. A process for producing polyamic acid microfine particles having functional groups at least on the particle surface by a synthetic route starting with a tetracarboxylic anhydride and a diamine compound, said process being characterized in that it comprises
(a) a first step which comprises providing a tetracarboxylic anhydride and a diamine compound at least one of which has said functional groups and preparing a first solution containing said tetracarboxylic anhydride and a second solution containing said diamine compound and
(b) a second step of mixing said first and second solutions together under ultrasonic agitation to precipitate polyamic acid microfine particles from the mixed solution.
2. A process for producing polyimide microfine particles having functional groups at least on the particle surface by a synthetic route starting with a tetracarboxylic anhydride and a diamine compound, said process being characterized in that it comprises
(a) a first step which comprises providing a tetracarboxylic anhydride and a diamine compound at least one of which has said functional groups and preparing a first solution containing said tetracarboxylic anhydride and a second solution containing said diamine compound,
(b) a second step which comprises mixing said first and second solutions together under ultrasonic agitation to precipitate polyamic acid microfine particles from the mixed solution, and
(c) a third step which comprises subjecting said polyamic acid microfine particles to imidation reaction to produce polyimide microfine particles.
3. Functional polyamic acid microfine particles having a mean particle diameter of 0.03xcx9c2 xcexcm as obtained by the process defined in the above paragraph 1.
4. Functional polyimide microfine particles having a mean particle diameter of 0.03xcx9c2 xcexcm as obtained by the process defined in the above paragraph 2.
The present invention is further directed to the following method of qualitative analysis.
5. A method for qualitative analysis of polyimide particles for functional groups on the surface by electron spectroscopy for chemical analysis (ESCA), said method being characterized in that it comprises a step of fluorinating the surface of said polyimide particles with a fluorinating agent reactive with said functional groups.